In construction machines such as hydraulic excavators and hydraulic cranes, the components thereof are driven by a hydraulic drive system. In such a hydraulic drive system, hydraulic oil is supplied to various actuators from a pump driven by an engine.
For example, Patent Literature 1 discloses a hydraulic drive system in which a booster pump driven by an electric motor is used in addition to a main pump driven by an engine. The booster pump is intended for increasing the amount of hydraulic oil supplied to actuators at high load.
Specifically, in the hydraulic drive system disclosed in Patent Literature 1, an alternator is mounted to the engine driving the main pump, and the alternator is connected to a battery. The alternator is a compact low power (e.g., a nominal voltage of 24 V) generator that includes a rotary shaft connected to the output shaft of the engine via a motive power transmitter, such as a belt. The battery is connected via a relay to the electric motor that drives the booster pump. The relay is turned ON at high load.